Technical Field
The invention relates to methods for assigning resource elements to various enhanced resource element groups. The invention is also providing the user equipment for performing the methods described herein.
Description of the Related Art
Long Term Evolution (LTE)
Third-generation mobile systems (3G) based on WCDMA radio-access technology are being deployed on a broad scale all around the world. A first step in enhancing or evolving this technology entails introducing High-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, also referred to as High Speed Uplink Packet Access (HSUPA), giving a radio access technology that is highly competitive.
In order to be prepared for further increasing user demands and to be competitive against new radio access technologies, 3GPP introduced a new mobile communication system which is called Long Term Evolution (LTE). LTE is designed to meet the carrier needs for high speed data and media transport as well as high capacity voice support for the next decade. The ability to provide high bit rates is a key measure for LTE.
The work item (WI) specification on Long-Term Evolution (LTE) called Evolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTE system represents efficient packet-based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. In LTE, scalable multiple transmission bandwidths are specified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieve flexible system deployment using a given spectrum. In the downlink, Orthogonal Frequency Division Multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference (MPI) due to a low symbol rate, the use of a cyclic prefix (CP) and its affinity to different transmission bandwidth arrangements. Single-carrier frequency division multiple access (SC-FDMA) based radio access was adopted in the uplink, since provisioning of wide area coverage was prioritized over improvement in the peak data rate considering the restricted transmit power of the user equipment (UE). Many key packet radio access techniques are employed including multiple-input multiple-output (MIMO) channel transmission techniques and a highly efficient control signaling structure is achieved in LTE Rel. 8/9.
LTE Architecture
The overall architecture is shown in FIG. 1 and a more detailed representation of the E-UTRAN architecture is given in FIG. 2. The E-UTRAN consists of an eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink Quality of Service (QoS), cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of downlink/uplink user plane packet headers. The eNodeBs are interconnected with each other by means of the X2 interface.
The eNodeBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (SGW) by means of the S1-U. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW). For idle state user equipments, the SGW terminates the downlink data path and triggers paging when downlink data arrives for the user equipment. It manages and stores user equipment contexts, e.g. parameters of the IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception.
The MME is the key control-node for the LTE access-network. It is responsible for idle mode user equipment tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation process and is also responsible for choosing the SGW for a user equipment at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation. It is responsible for authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to user equipments. It checks the authorization of the user equipment to camp on the service provider's Public Land Mobile Network (PLMN) and enforces user equipment roaming restrictions. The MME is the termination point in the network for ciphering/integrity protection for NAS signaling and handles the security key management. Lawful interception of signaling is also supported by the MME. The MME also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME from the SGSN. The MME also terminates the S6a interface towards the home HSS for roaming user equipments.
Component Carrier Structure in LTE (Release 8)
The downlink component carrier of a 3GPP LTE (Release 8) is subdivided in the time-frequency domain in so-called subframes. In 3GPP LTE (Release 8) each subframe is divided into two downlink slots as shown in FIG. 3, wherein the first downlink slot comprises the control channel region (PDCCH region) within the first OFDM symbols. Each subframe consists of a give number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), wherein each OFDM symbol spans over the entire bandwidth of the component carrier. The OFDM symbols thus each consists of a number of modulation symbols transmitted on respective NRBDL×NscRB subcarriers as also shown in FIG. 4.
Assuming a multi-carrier communication system, e.g. employing OFDM, as for example used in 3GPP Long Term Evolution (LTE), the smallest unit of resources that can be assigned by the scheduler is one “resource block”. A physical resource block (PRB) is defined as NsymbDL consecutive OFDM symbols in the time domain (e.g. 7 OFDM symbols) and NscRB consecutive subcarriers in the frequency domain as exemplified in FIG. 4 (e.g. 12 subcarriers for a component carrier). In 3GPP LTE (Release 8), a physical resource block thus consists of NsymbDL×NscRB resource elements, corresponding to one slot in the time domain and 180 kHz in the frequency domain (for further details on the downlink resource grid, see for example 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, section 6.2, available at http://www.3gpp.org and incorporated herein by reference).
One subframe consists of two slots, so that there are 14 OFDM symbols in a subframe when a so-called “normal” CP is used, and 12 OFDM symbols in a subframe when a so-called “extended” CP is used. For sake of terminology, in the following the time-frequency resources equivalent to the same NscRB consecutive subcarriers spanning a full subframe is called a “resource block pair”, or equivalent “RB pair” or “PRB pair”.
The term “component carrier” refers to a combination of several resource blocks in the frequency domain. In future releases of LTE, the term “component carrier” is no longer used; instead, the terminology is changed to “cell”, which refers to a combination of downlink and optionally uplink resources. The linking between the carrier frequency of the downlink resources and the carrier frequency of the uplink resources is indicated in the system information transmitted on the downlink resources.
Further Advancements for LTE (LTE-A)
The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequency spectrum for IMT-Advanced was decided, the actual available frequency bandwidth is different according to each region or country. Following the decision on the available frequency spectrum outline, however, standardization of a radio interface started in the 3rd Generation Partnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the Study Item description on “Further Advancements for E-UTRA (LTE-Advanced)” was approved. The study item covers technology components to be considered for the evolution of E-UTRA, e.g. to fulfill the requirements on IMT-Advanced. Two major technology components are described in the following.
Carrier Aggregation in LTE-A for Support of Wider Bandwidth
The bandwidth that the LTE-Advanced system is able to support is 100 MHz, while an LTE system can only support 20 MHz. Nowadays, the lack of radio spectrum has become a bottleneck of the development of wireless networks, and as a result it is difficult to find a spectrum band which is wide enough for the LTE-Advanced system. Consequently, it is urgent to find a way to gain a wider radio spectrum band, wherein a possible answer is the carrier aggregation functionality.
In carrier aggregation, two or more component carriers (component carriers) are aggregated in order to support wider transmission bandwidths up to 100 MHz. Several cells in the LTE system are aggregated into one wider channel in the LTE-Advanced system which is wide enough for 100 MHz even though these cells in LTE are in different frequency bands.
All component carriers can be configured to be LTE Rel. 8/9 compatible, at least when the aggregated numbers of component carriers in the uplink and the downlink are the same. Not all component carriers aggregated by a user equipment may necessarily be Rel. 8/9 compatible. Existing mechanism (e.g. barring) may be used to avoid Rel-8/9 user equipments to camp on a component carrier.
A user equipment may simultaneously receive or transmit one or multiple component carriers (corresponding to multiple serving cells) depending on its capabilities. A LTE-A Rel. 10 user equipment with reception and/or transmission capabilities for carrier aggregation can simultaneously receive and/or transmit on multiple serving cells, whereas an LTE Rel. 8/9 user equipment can receive and transmit on a single serving cell only, provided that the structure of the component carrier follows the Rel. 8/9 specifications.
Carrier aggregation is supported for both contiguous and non-contiguous component carriers with each component carrier limited to a maximum of 110 Resource Blocks in the frequency domain using the 3GPP LTE (Release 8/9) numerology.
Logical and Transport Channels
The MAC layer provides a data transfer service for the RLC layer through logical channels. Logical channels are either Control Logical Channels which carry control data such as RRC signaling, or Traffic Logical Channels which carry user plane data. Broadcast Control Channel (BCCH), Paging Control channel (PCCH), Common Control Channel (CCCH), Multicast Control Channel (MCCH) and Dedicated Control Channel (DCCH) are Control Logical Channels. Dedicated Traffic channel (DTCH) and Multicast Traffic Channel (MTCH) are Traffic Logical Channels.
Data from the MAC layer is exchanged with the physical layer through Transport Channels. Data is multiplexed into transport channels depending on how it is transmitted over the air. Transport channels are classified as downlink or uplink as follows. Broadcast Channel (BCH), Downlink Shared Channel (DL-SCH), Paging Channel (PCH) and Multicast Channel (MCH) are downlink transport channels, whereas the Uplink Shared Channel (UL-SCH) and the Random Access Channel (RACH) are uplink transport channels.
A multiplexing is then performed between logical channels and transport channels in the downlink and uplink respectively.
Layer 1/Layer 2 (L1/L2) Control Signaling
In order to inform the scheduled users about their allocation status, transport format and other data-related information (e.g. HARQ information, transmit power control (TPC) commands), L1/L2 control signaling is transmitted on the downlink along with the data. L1/L2 control signaling is multiplexed with the downlink data in a subframe, assuming that the user allocation can change from subframe to subframe. It should be noted that user allocation might also be performed on a TTI (Transmission Time Interval) basis, where the TTI length can be a multiple of the sub-frames. The TTI length may be fixed in a service area for all users, may be different for different users, or may even by dynamic for each user. Generally, the L1/2 control signaling needs only be transmitted once per TTI. Without loss of generality, the following assumes that a TTI is equivalent to one subframe.
The L1/L2 control signaling is transmitted on the Physical Downlink Control Channel (PDCCH). A PDCCH carries a message as a Downlink Control Information (DCI), which includes resource assignments and other control information for a mobile terminal or groups of UEs. In general, several PDCCHs can be transmitted in one subframe.
It should be noted that in 3GPP LTE, assignments for uplink data transmissions, also referred to as uplink scheduling grants or uplink resource assignments, are also transmitted on the PDCCH.
With respect to scheduling grants, the information sent on the L1/L2 control signaling may be separated into the following two categories, Shared Control Information (SCI) carrying Cat 1 information and Downlink Control Information (DCI) carrying Cat 2/3 information. For further information regarding the DCI formats and the particular information that is transmitted in the DCI, please refer to the technical standard or to LTE—The UMTS Long Term Evolution—From Theory to Practice, Edited by Stefanie Sesia, Issam Toufik, Matthew Baker, Chapter 9.3, incorporated herein by reference. The different DCI formats that are currently defined for LTE are as follows and described in detail in 3GPP TS 36.212, “Multiplexing and channel coding”, section 5.3.3.1 (available at http://www.3gpp.org and incorporated herein by reference).
Physical Downlink Control Channel (PDCCH) and Physical Downlink Shared Channel (PDSCH)
The physical downlink control channel (PDCCH) carries e.g. scheduling grants for allocating resources for downlink or uplink data transmission.
Each PDCCH is transmitted using one or more so called Control Channel Elements (CCEs). Each CCE corresponds to a set of Resource Elements (REs). In 3GPP LTE, at the moment one CCE consists of 9 Resource Element Groups (REGs), where one REG consists of four consecutive REs (consecutive in the frequency domain) excluding potential REs of reference signals. The resource elements occupied by reference symbols are not included within the REGs, which means that the total number of REGs in a given OFDM symbol depends on whether or not reference signals are present.
The PDCCH for the user equipments is transmitted on the first NsymbPDCCH OFDM symbols (usually either 1, 2 or 3 OFDM symbols as indicated by the PCFICH, in exceptional cases either 2, 3, or 4 OFDM symbols as indicated by the PCFICH) within a subframe, extending over the entire system bandwidth; the system bandwidth is typically equivalent to the span of a cell or component carrier. The region occupied by the first NsymbPDCCH OFDM symbols in the time domain and the NRBDL×NscRB subcarriers in the frequency domain is also referred to as PDCCH region or control channel region. The remaining NsymbPDSCH=2·NsymbDL−NsymbPDCCH OFDM symbols in the time domain on the NRBDL×NscRB subcarriers in the frequency domain is referred to as the PDSCH region or shared channel region (see below).
There are two special cases: in subframes containing MBSFN transmissions there may be 0, 1 or 2 symbols for control signaling, while for narrow system bandwidths (less than 10 resource blocks) the number of control symbols is increased, maybe to 2, 3 or 4, to ensure sufficient coverage at the cell border.
For a downlink grant on the physical downlink shared channel (PDSCH), the PDCCH assigns a PDSCH resource for (user) data within the same subframe. The PDCCH control channel region within a subframe consists of a set of CCE where the total number of CCEs in the control region of subframe is distributed throughout time and frequency control resource. Multiple CCEs can be combined to effectively reduce the coding rate of the control channel. CCEs are combined in a predetermined manner using a tree structure to achieve different coding rate.
In 3GPP LTE a PDCCH can aggregate 1, 2, 4 or 8 CCEs. The number of CCEs available for control channel assignment is a function of several factors, including carrier bandwidth, number of transmit antennas, number of OFDM symbols used for control and the CCE size, etc. Multiple PDCCHs can be transmitted in a subframe.
On a transport channel level, the information transmitted via the PDCCH is also referred to as L1/L2 control signaling. L1/L2 control signaling is transmitted in the downlink for each user equipment (UE). The control signaling is commonly multiplexed with the downlink (user) data in a subframe (assuming that the user allocation can change from subframe to subframe).
The physical downlink shared channel (PDSCH) is mapped to the remaining OFDM symbols within one subframe that are not occupied by the PDCCH. The PDSCH resources are allocated to the user equipments in units of resource blocks for each subframe.
FIG. 5 shows the exemplary mapping of PDCCH and PDSCH within a normal subframe (having 2·NsymbDL=14 OFDM symbols in the time domain), respectively a resource block pair (see magnification). In this exemplary case, the first NsymbPDCCH=2 OFDM symbols (PDCCH region) are used for L1/L2 control signaling, i.e. for signaling the PDCCH, and the remaining NsymbPDSCH=12 OFDM symbols (PDSCH region) are used for data. Within the resource block pairs of all subframes, cell-specific reference signals, CRS (Common Reference Signal), are transmitted. These cell-specific reference signals are transmitted on one or several of antenna ports 0 to 3. In this example, the CRS are transmitted from two antenna ports: R0 is from antenna port 0 and R1 is from antenna port 1.
FIG. 6 shows another example where the PDCCH and the PDSCH is mapped to a MBSFN subframe. The example of FIG. 6 is quite similar to FIG. 5, except for the MBSFN subframe not comprising common reference signals in OFDM symbols outside of the control channel region.
FIG. 7 illustrates a resource block pair and the CRS for antenna ports 0 to 3, as defined in the technical standard TS 36.211v10.4 Chapter 6.10, incorporated herewith by reference; in particular FIG. 6.10.1.2-1 where a normal cyclic prefix is assumed.
Release 10 introduces extensive support of UE-specific reference signals for demodulation of up to 8 layers corresponding to up to 8 antenna ports (in LTE Release 10, antenna ports 7-14). Correspondingly, the subframe also contains UE-specific reference signals, such as DMRS (DeModulation Reference Signal) that are used by the user equipments for demodulating the PDSCH. The DMRS are only transmitted within the resource blocks where the PDSCH for a certain user equipment is allocated. In the example of FIG. 8A, only DMRS ports 7-10 are shown since these are assumed to be sufficient for ePDCCH transmissions. It should be noted that at the moment it is not supported to use DMRS for the PDSCH when also using SFBC.
In addition, feedback of Channel-State-Information (CSI) is based on a set of reference signals—CSI reference signals (CSI-RS) which are relatively sparse in frequency but regularly transmitted from all antennas at the base station, while in general the UE-specific reference signals are denser in frequency but only transmitted when data is transmitted on the corresponding layer (see FIG. 8B). The CSI reference signal is transmitted in each physical antenna port or virtualized antenna port and is used for measurement purposes only.
A cell can be configured with one, two, four or eight CSI-RS ports. The exact CSI-RS structure, including the exact set of resource elements used for CSI-RS in a resource block, depends on the number of CSI-RS configured within the cell and may also be different for different cells. More specifically, within a resource-block pair there are 40 possible positions for the reference symbols of CSI-RS and, in a given cell, a subset of corresponding resource elements is used for CSI-RS transmission. In LTE Release 10, the CSI-RS are transmitted (if configured) on one or more of antenna ports 15-22.
FIGS. 8A and 8B illustrate the reference signals DMRS and CSI-RS for a resource block pair, according to one example.
For further information on the LTE physical channel structure in downlink and the PDSCH and PDCCH format, see St. Sesia et al., “LTE—The UMTS Long Term Evolution”, Wiley & Sons Ltd., ISBN 978-0-47069716-0, April 2009, sections 6 and 9. Additional information on the use of reference signals and channel estimation in 3GPP LTE can be found in section 8 of this book.
FIGS. 9 and 10 illustrate an exemplary mapping of resource elements to resource element groups within a physical resource block pair. As apparent therefrom, one resource element group comprises four adjacent resource elements within each OFDM symbol. Further, the resource elements that are used for the common reference signals are not used for defining a resource element group; in other words, when assigning the resource elements to resource element groups, the CRS REs are accounted for. Therefore, depending on the position of the CRS in the first OFDM symbol (which is cell specific), the mapping of REs to REGs is different. In particular, when comparing FIGS. 9 and 10, in the first OFDM symbol 0 the REs of subcarriers 0, 1, 3, 4, 6, 7 and 9, 10, the differences are apparent; e.g. resource element of subcarrier 1 and OFDM symbol 0, may be either assigned to REG 1 (FIG. 9) or may be used instead as a CRS (FIG. 10).
Space-Frequency Block Codes (SFBCs)
SFBC is a transmit diversity technique used in LTE. In LTE, transmit diversity is only defined for 2 and 4 transmit antennas and one data stream, referred to in LTE as one codeword since one transport block CRC is used per data stream. To maximize diversity gain the antennas typically need to be uncorrelated, so they need to be well separated relative to the wavelength or have different polarization. The SFBC diversity scheme may be used in LTE for the PBCH and PDCCH, and also for the PDSCH if it is configured in transmit diversity mode for a UE.
More specifically with regard to SFBC, if a physical channel in LTE is configured for transmit diversity operation using two eNodeB antennas, pure SFBC is used. SFBC is a frequency domain version of the well-known Space-Time Block Codes (STBCs), also known as Alamouti code. This family of codes is designed so that the transmitted diversity streams are orthogonal and achieve the optimal SNR with a linear receiver. Such orthogonal codes only exist for the case of two transmit antennas. Multiple subcarriers of OFDM lend themselves well to the application of SFBC.
For SFBC transmission in LTE, the symbols transmitted from the two eNodeB antenna ports on each pair of adjacent subcarriers are defined as follows:
      [                                                      y                              (                0                )                                      ⁡                          (              1              )                                                                          y                              (                0                )                                      ⁡                          (              2              )                                                                                      y                              (                1                )                                      ⁡                          (              1              )                                                                          y                              (                1                )                                      ⁡                          (              2              )                                            ]    =      [                                        x            1                                                x            2                                                            -                          x              2              *                                                            x            1            *                                ]  whereby y(p)(k) denotes the symbols transmitted from antenna port p on the kth subcarrier.
SFBC achieves robustness through frequency diversity by using different subcarriers for the repeated data on each antenna. Basically, an information symbol is transmitted on two different resource elements by using two distinct antennas (spatial component). Provided that the channel coefficient (amplitude/phase) for both versions is the same, the receiver can calculate the original symbol exploiting a diversity gain.
As mentioned above, the two versions of the information symbol are transmitted on adjacent subcarriers to be spaced closely in frequency; in said case, the channel coefficient for both versions can be assumed to be basically the same which improves the accurate regeneration of the information symbol using a simple receiver implementation, as shown by S. M. Alamouti “A Simple Transmitter Diversity Technique for Wireless Communication”, IEEE Journal on Selected Areas in Communications, Vol. 16, pp. 1451-1458, October 1998.
FIGS. 11 and 12 are similar to FIGS. 9 and 10 respectively, as far as both illustrate the RE-to-REG mapping for the PDCCH considering the different positioning of the CRS. Furthermore, FIGS. 11 and 12 also illustrate how SFBC may be applied to the PDCCH and to the PDSCH.
For the PDCCH, LTE works such that the SFBC pairs are located as adjacent as possible in the frequency domain within one OFDM symbol; as depicted in FIG. 11, 12 in OFDM symbol 0 the possible SFBC pairs are each shown in a dashed-line box. SFBC pairs can therefore be mapped to resource elements (k′,l′) and (k′+n,l′) in the same OFDM symbol, where k′ is the subcarrier index, l′ is the OFDM symbol number and nε{1, 2}. In other words, n=1 means that the SFBC pair is located at adjacent resource elements; n=2 means that the SFBC pair is located at resource elements that are spaced apart by two, i.e. one resource element (such as a CRS RE) in between. Therefore, the spacing is equivalent to 1 plus the number of REs between two REs forming an SFBC pair.
Similarly, with regard to the PDSCH, SFBC pairs can be mapped to resource elements (k′,l′) and (k′+n,l′) in the same OFDM symbol, where k′ is the subcarrier index, l′ is the OFDM symbol number and nε{1, 2}. In other words, n=1 means that the SFBC pair needs to be adjacent resource elements; n=2 means that the SFBC pair may be of resource elements that are spaced apart by two, i.e. one resource element (such as a CRS RE) in between. FIG. 11 exemplary discloses SFBC pairs in dashed-line boxes in OFDM symbol 1 and 6 for n=1, and FIG. 12 in the PDCCH region exemplary illustrates SFBC pairs in dashed-line boxes for n=2.
LTE also allows a transmit diversity approach known as a combination of frequency switched transmit diversity (FSTD) with SFBC. FSTD schemes transmit symbols from each antenna on a different set of subcarriers. More information on FSTD is given in Chapter 11.2.2.1 of LTE—The UMTS Long Term Evolution—From Theory to Practice, Edited by Stefanie Sesia, Issam Toufik, Matthew Baker, Chapter 9.3, incorporated herein by reference.
Enhanced-PDCCH
Currently under discussion is to introduce an Enhanced PDCCH (ePDCCH), which is transmitted based on UE-specific reference signals. In order to efficiently use UE-specific reference signals, the mapping of Enhanced-PDCCH is preferred to be allocated in the PDSCH region, as depicted in FIG. 13. In order not to blind-decode the whole bandwidth, it is assumed that the search space of ePDCCH would be limited within a set of PRBs pairs. The set of PRBs pairs can be first configured by higher layer signaling, or at least is assumed to be known by the receiver prior to trying to detect any ePDCCH.
Details for the ePDCCH are currently under discussion and thus not yet decided. Therefore, the following assumptions are made as examples only for illustration and explanatory purposes. In general it may be assumed that a similar approach will be used as for the PDCCH. For example, it may be assumed that the ePDCCH consists of an aggregation of one or more control channel elements; in the following they may be exemplary called Enhanced Control Channel Elements (eCCEs). Furthermore, an eCCE may be formed from resource element groups that are mapped to resource elements in the time/frequency grid; they may be exemplary called Enhanced Resource Element Groups (eREGs).
FIG. 13 schematically discloses the subframe content regarding PDCCH, ePDCCH and PDSCH, and further illustrates that for the ePDCCH 8 different eREG are exemplary assumed.
At present, there is no agreed definition as to how the resource element to resource element group mapping is going to be for the ePDCCH being in the PDSCH region.
The RE-to-eREG mapping for the ePDCCH (i.e. generally within or at least including REs from the PDSCH region) should allow for a SBFC transmission to achieve diversity, and advantageously should furthermore allow the application of the same mapping regardless of whether a diversity transmission is utilized or not.